Method of installing a reverse taper fastener in workpieces

ABSTRACT

A reverse taper fastener system including a fastener pin having an elongate bearing section adapted to extend through holes in the work pieces where the bearing section tapers inwardly from the leading end toward the trailing end of the bearing section, having an enlarged head integral with the trailing end of the bearing section, and a pintail section at the leading end of the fastener pin which may carry an expansion collet for expanding the holes from a diameter smaller than the bearing section to a diameter larger than same for installing the fastener. The disclosure also comprehends the method of installing the fastener as well as the method of manufacturing the fastener.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division, of application Ser. No. 554,762, filed Mar. 3, 1975,now U.S. Pat. No. 4,012,885.

BACKGROUND OF THE INVENTION

Many highly stressed fastener joints are used today, especially in theaerospace industry. Such fastener joints generally use a fastener with ahead at one end, a bearing section which can be extended through theholes in the work pieces integral with the head and an engagementsection at the opposite end of the bearing section which is designed tobe engaged by a locking device such as a nut or collar to maintain thefastener in position. Two important criteria are usually followed insuch fastener joints, the first being the maintenance of good bearingcontact between the fastener and the work pieces and the second beingthe keeping of the weight of the fastener joint at a minimum.

Generally, two types of fasteners are used in these fastener joints. Thefirst type of fastener is a fastener having a substantially constantdiameter bearing section that is placed through substantially constantdiameter holes in the work pieces and the second type is a fastener witha tapered bearing section that tapers outwardly from the engagementsection toward the head which is placed in a correspondingly taperedhole through the work pieces. While tapered fasteners such as thosedisclosed in U.S. Pat. Nos. 3,034,611 and 3,304,109 do produce fastenerjoints with good bearing contact between the bearing section of thefastener and the work pieces, the major difficulty with using suchfastener systems is that it is extremely difficult to produce thecorrect tapered hole through the work pieces. It will also be noted thatsuch tapered fasteners tend to be forced out of the holes, head endfirst, thereby requiring a strong locking device such as a nut or collarto retain the fastener in place. When using a constant diameter bearingsection fastener system, the hole forming process is considerablysimplified, however, it is more difficult to obtain good bearing betweenthe bearing section of the fastener and the work pieces. The requirementof these prior art systems of a locking device such as a nut or collarhas resulted in the systems remaining relatively heavy thereby reducingthe overall pay load of the structure in which they are used.

Techniques have also been developed for increasing the fatigue life ofthe joint. One of these techniques is commonly known as coldworkingwherein the hole is expanded to such an extent that the metalimmediately surrounding the holes where the localized expansion occursis stressed beyond its compressive yield point and after which the holeis permitted to return or rebound toward its original diameter toestablish a compressive stress gradient immediately surrounding thehole. Such coldworking techniques are disclosed in U.S. Pat. Nos.3,434,327; 3,566,662; and 3,805,578. Another technique which has beenused in this regard is commonly known as an interference fit where thediameter of the bearing section of the fastener is greater than thenominal diameter of the holes in which the fastener is fitted. Thetechniques of coldworking and interference fit have been combined inspecial fasteners such as disclosed in U.S. Pat. Nos. 3,578,267 and3,779,127. It will be seen that the fasteners used in these techniquesalso require the locking device such as a nut or collar thereon toretain the fastener in place.

SUMMARY OF THE INVENTION

These and other problems and disadvantages associated with the prior artare overcome by the invention disclosed herein in that a reverse taperedbearing section is provided on the fastener which serves to retain thefastener in position within the work pieces while at the same timeinsuring good bearing contact between the bearing section of thefastener and the work pieces. This allows the locking device such as thenut or collar to be completely eliminated in a shear application and thelocking device to be reduced in weight in tension applications. Theinvention is installed by expanding the holes from a diameter less thanthe major diameter of the bearing section of the fastener out to anexpanded diameter greater than the major diameter of the bearing sectionand inserting the bearing section while the holes are expanded. Theholes are allowed to rebound around the bearing section to engage same.The resulting joint is not only an interference fit but also has beencoldworked to produce the ultimate strength and fatigue life. Aninstallation using the invention is greatly simplified, especially whereno locking device is required thereby reducing the installation cost ofthe fastener of the invention.

The apparatus of the invention includes a fastener which has an elongatebearing section adapted to extend through aligned holes in work pieceswith a head integral with one end of the bearing section. The bearingsection tapers inwardly from its leading end toward its trailing end sothat when the holes through the work pieces are expanded to allow thefastener to be installed, the holes recover to a diameter smaller thanthe major diameter of the bearing section so that an interference fit isobtained. The compressive force gradient about the hole acts on at leasta major portion of the bearing surface on the bearing section of thefastener to try to force the fastener through the holes in the directionaway from the head of the fastener so that the work pieces themselvesserve to lock the fastener in place and reduce or eliminate the externalforce required to retain the fastener in the holes. If significanttension forces are present in the fastener joint, a nut or other lockingdevice may be installed on an engagement section on the leading end ofthe bearing section of the fastener to absorb the tension load.

These and other features and advantages of the invention are disclosedherein and will become more clearly understood upon consideration of thefollowing specification and accompanying drawings wherein likecharacters of reference designate corresponding parts throughout theseveral views and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded elevational view of a first embodiment of theinvention;

FIG. 2 is an exploded elevational view of a second embodiment of theinvention;

FIG. 3 is an exploded elevational view of a third embodiment of theinvention;

FIG. 4 is an elevational view shown partly in cross-section of a fourthembodiment of the invention;

FIG. 5 is a partial elevational view of a modification of the secondembodiment of the invention;

FIG. 6 is an elevational view shown partly in cross-section of a specialnut for use with the third embodiment of the invention shown in FIG. 3;

FIG. 7 is an end view of the nut of FIG. 6;

FIG. 8 is an exploded side elevational view of a modification of thethird embodiment of the invention seen in FIG. 3;

FIGS. 9-13 illustrate the installation of the first embodiment of theinvention;

FIG. 14 shows the second embodiment of the invention shown in FIG. 2installed;

FIG. 15 illustrates the third embodiment of the invention shown in FIG.3 being installed;

FIG. 16 illustrates the nut of FIGS. 6 and 7 installed on the fastenerin FIG. 15;

FIG. 17 is a view illustrating the invention of FIG. 8 installed;

FIG. 18 is a view illustrating the installation of the fourth embodimentof the invention shown in FIG. 4;

FIG. 19 is a cross-sectional view of a joint incorporating a firstmodification of the first embodiment of the invention seen in FIG. 1;

FIG. 20 is a cross-sectional view of a joint incorporating a secondmodification of the first embodiment of the invention seen in FIG. 1;

FIGS. 21-23 illustrate a method of manufacturing the invention;

FIG. 24 is an elevational view of a third modification of the firstembodiment of the invention seen in FIG. 1; and,

FIG. 25 is a view illustrating the invention of FIG. 24 being installed.

These figures and the following detailed description herein disclosespecific embodiments of the invention, however, it is to be understoodthat the inventive concept is not limited thereto and may be embodied inother forms.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring to FIG. 1, it will be seen that the first embodiment of theinvention includes a fastener pin 10 and a hole expansion collet 11adapted to be carried by the fastener pin 10 as the fastener pin 10 isinstalled in the holes through the work pieces as will become moreapparent. The fastener pin 10 includes generally a fastener portion 12and a pintail portion 14 coaxially connected to the fastener portion 12about the pin axis A_(p) through a breakneck section 15. It will furtherbe seen that the pin 10 has a leading end 16 and a trailing end 18. Thefastener portion 12 includes a bearing section 20 which is integral withthe breakneck section 15 at its leading end and integral with anenlarged head 21 at its trailing end. The head 21 illustrated is of thecountersunk type, however, it is to be understood that different headstyles can be used depending on the particular application withoutdeparting from the inventive concept. The bearing section 20 defines anexternal bearing surface 22 thereon which is concentrically arrangedabout the axis A_(p) and tapers inwardly uniformly from the leading endof the bearing section 20 to the trailing end thereof. The leading endof the bearing surface 22 has a major prescribed diameter d₁ and thetrailing end of the surface 22 has a minimum prescribed diameter d₂ aswill be more fully explained. It will thus be seen that the bearingsurface 22 has a reverse taper thereon from that normally associatedwith fasteners. A leading end of the bearing section 20 defines anannular driving face 24 thereon about the breakneck section 15 which isarranged normal to the axis A_(p) of the pin 10. It will also be notedthat the fastener portion 12 has an effective maximum grip length L₁which is longer than the length L₂ of the bearing section 20 as isnormally associated with fasteners with countersunk heads. For anexposed head fastener portion, the grip length L₁ would be equal to thelength L₂ of the bearing section 20.

The pintail portion 14 of the fastener pin 10 defines a pulling section40 on the leading end thereof and a support section 41 on the trailingend thereof which is integral with the breakneck station 15. It willalso be noted that the pintail portion 14 has an effective length L₃ aswill become more apparent. The pulling portion 40 has a configurationnormally associated with lockbolt type fasteners with alternating ridges42 and grooves 44 to be gripped by the pulling nose assembly of aconventional lockbolt installation tool as will be more fully explained.It will be noted that the pulling section 40 has a maximum diameter d₃such that the pulling section 40 can be inserted into the nose assemblyof the lockbolt pulling gun. The trailing end of the pulling section 40is integral with the leading end of the support section 41 so that thefastener pin 10 is a unitary structure. The support section 41 has acylindrical support surface 45 thereon which is concentric about theaxis A_(p) with the support surface 45 having a substantially constantdiameter d₄ less than the diameter d₁ as will become more apparent. Thebreakneck section 15 defines a breakneck groove 55 therein to produce areduced diameter frangible section 56 with diameter d₅ smaller than theminimum diameter of the pulling section 40 to insure that the fastenerpin 10 will fracture at the frangible section 56.

The collect 11 is removably received on the pintail portion 14 andsupported by the support section 41 to expand the holes through the workpieces immediately preceding the bearing section 20 as the fastener pin10 is installed. The collect 11 has an annular side wall 80 concentricabout the collect central axis A_(c) with a leading end 81 and atrailing end 82. The side wall 80 defines a cylindrical passage 84therethrough with a diameter d₆ which is just sufficient for the collect11 to be slidably received onto the support surface 45 of the pintailportion 14 on pin 10 and be in bearing support thereon. The diameter d₆is usually no more than 0.001 inch greater than the diameter d₄ of thesupport surface 45. The collect 11 has a length L₄ which issubstantially equal to the sum of the length of the support section 41and the breakneck section 15.

The side wall 80 includes a leading pilot section 85 and a trailingexpansion section 86 integral with the trailing end of the pilot section85. The pilot section 85 defines a cylindrical pilot surface 88 on theoutside thereof concentric about the collect central axis A_(c). Thepilot surface 88 has an outside diameter d₈ which is sufficient tolocate the collet 11 coaxially with the centerline of the holes throughthe work pieces when the surface 88 extends into the holes as willbecome more apparent. Normally, the diameter d₈ of the pilot surface 88is in the order of 0.001 inch less than the initial hole diameter aswill be explained.

The expansion section 86 includes a leading expansion surface 89, anintermediate land surface 90 and a trailing contraction surface 91, allconcentric about the central axis A_(c) of the collet 11. The expansionsurface extends outwardly from the diameter d₈ of the pilot surface 88to a major diameter d₉ at its trailing end. The diameter d₉ is greaterthan the initial hole diameter through the work pieces by the amountwhich it is desired to expand the holes. It will be noted that thediameter d₉ must be greater than the major diameter d₁ of the bearingsection 20 as will become more apparent. If optimum coldworking isdesired, the diameter d₉ is usually 2-10% greater than the hole diameterof the initial hole diameter through the work pieces as set forth byknown data and depends on the material of the work pieces and thedesired final diameter of the holes. While different shapes may beprovided for the expansion surface 89, the surface 89 illustrated issemi-ellipsoidal in shape where the included angle between the tangentto the surface 89 at any point decreases from the leading to thetrailing end of the surface 89. It will be seen that such shapes ofsurface 89 produces an exponentially increasing mechanical advantage atthe surface 89/hole interface from the leading to the trailing end ofthe surface 89. This serves to minimize the frictional interface betweenthe surface 89 which, in turn, reduces the force required to move thesurface 89 through the holes. The land surface 90 is cylindrical withthe maximum expansion diameter d₉ and is smoothly joined to theexpansion surface 89 at its leading end. The contraction surface 91 issmoothly joined to the trailing end of the land surface 90 and tapersinwardly from the diameter d₉ of the land surface 90 to a trailing minordiameter d₁₀ which is at least as large as the major diameter d₁ on thebearing section 20 of fastener pin 10 as will become more apparent. Thetrailing end of the side wall 80 defines a rearwardly facing annulardriving face 92 thereon which is concentrically located about the axisA_(c) and lies in a plane normal to the axis. The trailing driven face92 on the collet 11 is adapted to be engaged by the leading driving face24 on the bearing section 20 of the fastener pin 10 to cause the collet11 to be forced through the holes in the work pieces by pulling on thepulling section 40 of the pintail portion 14, as will be explained.

Referring to FIG. 19, a first modification of the fastener pin isillustrated after it is installed and designated 10'. The onlydifference between the fastener pin 10' in FIG. 19 and the pin 10 ofFIG. 1 is in the external bearing surface on the bearing section 20which has been designated as 22'. The bearing surface 22' has a leadingreverse taper surface section 22_(RT) located on the leading portion ofthe bearing section 20 and a trailing constant diameter surface section22_(CD) extending between the trailing end of the leading surfacesection 22_(RT) and the head 21 of the support pin 10'. The leadingreverse taper surface section 22_(RT) has a length L_(RT) less than thelength of holes H or the material thickness T and the surface section22_(CD) has a length L_(CD). The reverse taper surface section 22_(RT)tapers inwardly from the leading diameter d₁ at the leading end of thebearing section 20 to the trailing minor diameter d₂ at the trailing endof the surface section 22.sub. RT. It will also be noted that thesurface section 22_(CD) has the substantially constant diameter d₂ alongits length. Preferably, the length L_(RT) at the surface section 22_(RT)should be a major portion of the total thickness of the work pieces Pthrough which the fastener pin 10' extends to insure that the fastenerpin 10' will be held in position by the reverse taper subsurface 22_(RT)as set forth hereinabove. The fastener 10' will be installed in the samemanner as the fastener 10. The material of the work pieces P about theholes H would contract and be in bearing contact with the reverse tapersubsurface 22_(RT) as well as the constant diameter subsurface 22_(CD).

Referring to FIG. 20, a second modification of the fastener pin isillustrated after it is installed and designated 10". The onlydifference between the pastener pin 10" in FIG. 19 and the pin 10 ofFIG. 1 is in the external bearing surface on the bearing section 20which has been designated as 22". The bearing surface 22" has a leadingreverse taper subsurface 22_(RT) located on the leading portion of thebearing section 20 and a forward taper subsurface 22_(FT) extendingbetween the trailing end of the leading subsurface 22_(RT) and the head21 of the support pin 10". The leading reverse taper subsurface 22_(RT)has a length L_(RT) less than the length of holes H or materialthickness T and the subsurface 22_(FT) has a length L_(FT). The reversetaper subsurface 22_(RT) tapers inwardly from the leading diameter d₁ atthe leading end of the bearing section 20 to the trailing minor diameterd₂ at the trailing end of the subsurface 22_(RT). It will also be notedthat the trailing forward taper subsurface 22_(FT) tapers uniformlyoutwardly from the minor diameter d₂ to a trailing secondary majordiameter d_(SD) at the trailing end of the bearing section 20. Thediameter d_(SD) is larger than diameter d₂ and is usually smaller thanthe major expansion diameter d₉ of collet 11 used to install fastener10". Preferably, the length L_(RT) at the subsurface 22_(RT) should be amajor portion of the total thickness of the work pieces P through whichthe fastener pin 10" extends to insure that the fastener pin 10" will beheld in position by the reverse taper subsurface 22_(RT) as set forthhereinabove. The fastener 10" would be installed in the same manner asthe fastener 10. The material of the work pieces P about the holes Hwould contract in and be in bearing contact with the reverse tapersubsurface 22_(RT) as well as the forward taper subsurface 22_(FT).

Referring to FIG. 24, a third modification of the first embodiment ofthe fastener pin is shown and designated 10_(I). The modifying fastenerpin 10_(I) has the expansion collet integral with the trailing end ofthe pintail portion 14_(I) as an expansion member 11_(I). The expansionmember 11_(I) replaces the collet and support section of the pintail asshown in FIG. 1. The expansion member 11_(I) has a leading pilot section85_(I) corresponding to the pilot section 85 on the collet 11 and atrailing expansion section 86_(I) integral with the trailing end of thepilot section 85_(I) with the expansion section 86_(I) correspondinggenerally to the expansion section 86 on the collet 11. The pilotsection 85_(I) defines a cylindrical pilot surface 88_(I) on the outsidethereof concentric about the central axis A_(p) of the pin 10_(I). Thesurface 88_(I) serves the same purpose as the surface 88 on the collet11. The expansion section 86_(I) includes a leading expansion surface89_(I), an intermediate land surface 90_(I) and a trailing contractionsurface 91_(I), all concentric about the central axis A_(p) of the pin10_(I). The surfaces 89_(I), 90_(I) and 91_(I) correspond in size andfunction to the surfaces 89, 90 and 91 of the collet 11. The leading endof the expansion member 11_(I) is integral with the trailing end of thepulling section 40 of pintail portion 14_(I).

The breakneck section 15_(I) is provided between the trailing end of theexpansion member 11_(I) and the leading end of the bearing section 20 onthe fastener portion 12. The breakneck section 15_(I) includes a groove55_(I) which leaves a reduced diameter frangible section 56_(I)connecting the trailing end of the expansion member 11_(I) with theleading end of the bearing section 20. The frangible section 56_(I)serves the same purposes as frangible section 56 in the fastener pin 10.The remaining components of the fastener pin 10_(I) are the same as thefastener pin 10 and the same reference numerals applied to the fastenerpin 10 are also applied to the fastener pin 10_(I). The trailingdiameter d₁₀ ' of the expansion member 11_(I) is sufficiently largerthan the leading diameter d₁ of the bearing section 20 and the widthW_(I) of the breakneck groove 55_(I) is sufficiently small to permit theleading end of the bearing section 20 to pass into the holes H as seenin FIG. 25 before the diameter of the holes have recovered to a diametersmaller than the diameter d₁.

SECOND EMBODIMENT

Referring to FIG. 2, it will be seen that the second embodiment of theinvention is to be used similarly to the first embodiment and includes afastener pin 110 and a hole expansion collet 111 adapted to be carriedby the fastener pin 110 as the fastener pin 110 is installed in theholes through the work pieces. The fastener pin 110 includes generally afastener portion 112 and a pintail portion 114 coaxially connected tothe fastener portion 112 about the pin axis A_(p) through a breaknecksection 115. It will further be seen that the pin 110 has a leading end116 and a trailing end 118. The fastener portion 112 includes a bearingsection 120 which is integral with the breakneck section 115 at itsleading end and integral with a head 121 at its trailing end. The head121 illustrated is of the countersunk type.

The bearing section 120 defines a primary external bearing surface 122thereon which is concentrically arranged about the axis A_(p) and tapersinwardly uniformly from the leading end of the bearing section 120 tothe trailing end thereof. The leading end of the bearing surface 122 hasthe major prescribed diameter d₁ and the trailing end of the surface 122has the minimum prescribed diameter d₂ similarly to surface 22. Thebearing section 120 also defines a secondary grip adjustment surface 125concentric about the pin axis A_(p) immediately leading the primarybearing surface 122. The trailing end of surface 125 is smoothly joinedto the leading end of the surface 122 and uniformly tapers outwardly andforwardly therefrom from the leading diameter d₁ of surface 122 to alarger diameter d₁₁ no larger than the maximum expansion diameter d₉ ofcollet 111 as will be explained. The leading end of the tapered gripadjustment surface 125 may be smoothly joined to a narrow cylindricalland lead-in surface 126 with the diameter d₁₁. It will thus be seenthat both the primary bearing surface 122 and the grip adjustmentsurface 125 have a reverse taper thereon from that normally associatedwith fasteners. The leading end of the bearing section 120 defines thedriving face 124 thereon about the breakneck section 115 which isarranged normal to the axis A_(p) of the pin 110. The fastener portion110 has an effective grip range from the minimum grip length L_(min) atthe juncture of surfaces 122 and 125 to the maximum grip length L_(max)at the land lead-in surface 126.

The pintail portion 114 is the same as pintail portion 14 of fastenerpin 10 with the pulling section 140 and support section 141. Pintailportion 114 serves the same function as portion 14 on pin 10.

The collet 111 is removably received on the pintail portion 114 andsupported by the support section 141 to expand the holes through thework pieces immediately preceding the bearing section 120 as thefastener pin 110 is installed. The collet 111 has an annular side wall180 concentric about the collet central axis A_(c) with a leading end181 and a trailing end 182. The side wall 180 defines a cylindricalpassage 184 therethrough with diameter d₆ which is just sufficient forthe collet 111 to be slidably received onto the support surface 145 ofthe pintail portion 141 and be in bearing support thereon.

The side wall 180 includes a leading pilot section 185 and a trailingexpansion section 186 integral with the trailing end of the pilotsection 185. The pilot section 185 defines a cylindrical pilot surface188 on the outside thereof concentric about the collet central axisA_(c). The pilot surface 188 has an outside diameter d₈ which issufficient to locate the collet 111 coaxially with the centerline of theholes through the work pieces when the surface 188 extends into theholes.

The expansion section 186 includes a leading expansion surface 189 and atrailing land surface 190 both concentric about the central axis A_(c)of the collet 111. The expansion surface extends outwardly from thediameter d₈ of the pilot surface 188 to a major diameter d₉ at itstrailing end. The diameter d₉ is greater than the initial hole diameterthrough the work pieces by the amount which it is desired to expand theholes. It will be noted that the diameter d₉ must be greater than themajor diameter d₁ of the bearing section 120. The land surface 190 iscylindrical with the maximum expansion diameter d₉ and is smoothlyjoined to the expansion surface 189 at its leading end. The diameters ofthe land surface 190 on the collet 111 is substantially that of the landsurface 126 on bearing section 120 so that the surface 126 forms acontinuation of the surface 125 as will become more apparent. Thetrailing end of the side wall 180 defines a rearwardly facing annulardriven face 192 thereon which is concentrically located about the axisA_(c) and lies in a plane normal tothe axis. The trailing driven face192 on the collet 111 is adapted to be engaged by the leading drivingface 124 on the bearing section 120 of the fastener pin 110 to cause thecollet 111 to be forced through the holes in the work pieces by pullingon the pulling section 140 of the pintail portion 114.

FIG. 5 illustrates a modification of the grip adjustment surface on theleading end of bearing section 120 and is designated 125'. The surface125' defines a plurality of annular steps 128 which serve to prevent thesurface 125' from being forced back through the holes without broachingsame.

THIRD EMBODIMENT

Referring to FIG. 3, it will be seen that the third embodiment of theinvention includes a fastener 210 and the hole expansion collet 11adapted to be carried by the fastener pin 210 similarly to pin 10. Thepin 210 is designed for applications primarily in shear but with sometension loading. The fastener pin 210 includes generally a fastenerportion 212 and a pintail portion 214 coaxially connected to thefastener portion 212 about the pin axis A_(p) through a breaknecksection 215. It will further be seen that the pin 210 has a leading end216 and a trailing end 218. The fastener portion 212 includes a bearingsection 220 integral with the head 221 at its trailing end. The head 221is illustrated as the countersunk type.

The bearing section 220 defines an external bearing surface 222 thereonwhich is concentrically arranged about the axis A_(p) and tapersinwardly uniformly from the leading end of the bearing section 220 tothe trailing end thereof. The leading end of the bearing surface 222 hasthe major prescribed diameter d₁ and the trailing end of the surface 222has the minimum prescribed diameter d₂ similar to surface 22. It willthus be seen that the bearing surface 222 has a reverse taper thereonfrom that normally associated with fasteners. The leading end of thebearing section 220 defines a forwardly facing annular driving face 224thereon which is arranged normal to the pin axis A_(p). It will also benoted that the fastener portion 212 has an effective grip length L₁similar to pin 10.

A reduced diameter engagement section 225 is integral with the leadingend of the bearing section 220 and coaxial therewith about axis A_(p).The section 225 has the diameter d₄ along its length L₅ and is providedwith external threads 226. The threads 226 have a crest land surface 228of diameter d₄ to support collet 111 as will become more apparent. Itwill be seen that diameter d₄ is smaller than diameter d₁. The leadingend of engagement section 225 is integral with breakneck section 215.

The pintail portion 214 of the fastener pin 210 defines a pullingsection 240 on the leading end thereof and a support section 241 on thetrailing end thereof which is integral with the breakneck section 215.It will also be noted that the pintail portion 214 has effective lengthL₃ as will become more apparent. The pulling portion 240 has theconfiguration normally associated with lockbolt type fasteners withalternating ridges 242 and grooves 244 to be gripped by the pulling noseassembly of a conventional lockbolt installation tool. It will be notedthat the pulling section 240 has a maximum diameter d₃ such that thepulling section 240 can be inserted into the nose assembly of thelockbolt pulling gun. The trailing end of the pulling section 240 isintegral with the leading end of the support section 241 so that thefastener pin 10 is a unitary structure. The support section 241 has aleading foreshortened cylindrical support surface 245 thereon which isconcentric about the axis A_(p) with the support surface 245 having thesubstantially constant diameter d₄ so that surface 245 forms acontinuation of the crest land surfaces 228 on threads 226 on engagementsection 225 to support collet 11 thereon. The sum of the lengths of theengagment section 225, breakneck section 215 and support section 241 isapproximately the length of collet 11.

FIGS. 6 and 7 illustrate a special nut 300 for use on engagement section225 of fastener pin 210. The nut 300 has an annular side wall 301 withinternal threads 302 complimentary to threads 226 on engagement section225. This allows nut 300 to be screwed onto engagement section 225 afterthe pintail portion 214 has been fractured therefrom. Nut 300 also hasan annular flange 304 integral with the trailing end of side wall 301and normal to nut axis A_(N). An annular rearwardly facing lip 305concentric about axis A_(N) is integral with the outside edge of flange304 and defines an annular rearwardly facing bearing face 306 on thetrailing end thereof adapted to bear against the work pieces about thebearing section 220 as will become more apparent. The lip 305 defines anopening 308 therein with a diameter d₁₂ larger than diameter d₁ and theflange 304 is spaced forward of the face 306 a distance L₆ greater thanthe grip variation of pin 210 so that the leading end of bearing section220 will fit therein.

FIG. 8 shows a fastener pin 210 with a modified engagement sectionthereon designated 225'. Dimensionally, the section 225' corresponds tosection 225. Rather than threads, section 225' is designed for use witha swagable collar SC seen in FIG. 17 and has alternating locking grooves226' and lands 228'. The lands 228' have the diameter d₄ to supportcollet 11.

FOURTH EMBODIMENT

Referring to FIG. 4, it will be seen that the fourth embodiment of theinvention includes a fastener pin 410 and a hole expansion collet 411adapted to be carried by the fastener pin 410 as the fastener pin 410 isinstalled in the holes through the work pieces. The fastener pin 410includes generally a fastener portion 412 and a pintail portion 414coaxially connected to the fastener portion 12 about the pin axis A_(p)through a breakneck section 415. It will further be seen that the pin410 has a leading end 416 and a trailing end 418. The fastener portion412 includes a bearing section 420 integral with an engagement section425 at its leading end and integral with head 421 at its trailing end.The head 421 illustrated is of the protruding type, however, it is to beunderstood that different head styles can be used depending on theparticular application without departing from the inventive concept.

The bearing section 420 defines an external bearing surface 422 thereonwhich is concentrically arranged about the axis A_(p) and tapersinwardly uniformly from the leading end to the trailing end thereof. Theleading end of the bearing surface 422 has a major prescribed diameterd₁ and the trailing end of the surface 422 has a minimum prescribeddiameter d₂ as will be more fully explained. It will thus be seen thatthe bearing surface 422 has a reverse taper thereon of that normallyassociated with fasteners. The leading end of bearing section 420defines a re-expansion lead-in surface 426 that tapers outwardly fromthe diameter d₁₄ of engagement section 425 at its leading end to thediameter d₁ at its trailing end where it is smoothly joined with bearingsurface 422.

The engagement section 425 has major diameter d₁₄ corresponding to astandard engagement section for the particular size fastener and hasstandard external threads 428 adapted to receive a standard nut (notshown) thereon. The leading end of the engagement section 425 defines anannular driving face 424 thereon about the breakneck section 415 whichis arranged normal to the axis A_(p) of the pin 410. The pintail section414 is similar to pintail portion 14 on pin 10 with pulling section 440and support section 441.

The collet 411 is removably received on the pintail portion 414 andsupported by the support section 441 to expand the holes through thework pieces immediately preceding the engagement section 425 as thefastener pin 410 is installed. The collet 411 has an annular side wall480 concentric about the collet central axis A_(c) with a leading end481 and a trailing end 482. The side wall 480 defines a cylindricalpassage 484 therethrough with a diameter d₆ which is just sufficient forthe collet 411 to be slidably received onto the support surface 445 ofthe pintail portion 414, and be in bearing support thereon.

The side wall 480 includes a leading pilot section 485 and a trailingexpansion section 486 integral with the trailing end of the pilotsection 485. The pilot section 485 defines a cylindrical pilot surface488 on the outside thereof concentric about the collet central axisA_(c). The pilot surface 488 has an outside diameter d₈ which issufficient to locate the collet 411 coaxially with the centerline of theholes through the work pieces when the surface 488 extends into theholes as will become more apparent.

The expansion section 486 includes a leading expansion surface 489, anintermediate land surface 490 and a trailing contraction surface 491,all concentric about the central axis A_(c) of the collet 411. Theexpansion surface extends outwardly from the diameter d₈ of the pilotsurface 488 to a major diameter d₉ at its trailing end. The diameter d₉is greater than the initial hole diameter through the work pieces by theamount which it is desired to expand the holes. It will be noted thatthe diameter d₉ must be greater than the major diameter d₁ of thebearing section 420 as will become more apparent. While different shapesmay be provided for the expansion surface 489, the surface 489illustrated is semi-ellipsoidal in shape. The land surface 490 iscylindrical with the maximum expansion diameter d₉ and is smoothlyjoined to the expansion surface 489 at its leading end. The contractionsurface 491 is smoothly joined to the trailing end of the land surface490 and tapers inwardly from the diameter d₉ of the land surface 490 toa trailing minor diameter d₁₀. The trailing end of the side wall 480defines a rearwardly facing annular driven face 492 thereon which isconcentrically located about the axis A_(c) and lies in a plane normalto the axis. The trailing driven face 492 on the collet 11 is adapted tobe engaged by the leading driving face 424 on the engagement section 425of the fastener pin 410 to cause the collet 411 to be forced through theholes in the work pieces by pulling on the pulling section 440 of thepintail portion 414. A clearance surface 494 may connect the face 492with contraction surface 491 and angle forwardly of face 492 to clearthreads 428 and prevent damage thereto as the pin 410 is installed.

OPERATION

Generally, all the various embodiments of the invention disclosed hereinare installed in a similar manner and therefore only the installation ofthe first embodiment of the invention will be described in detail, withthe differences in installation of the other embodiments specificallypointed out. The installation of the first embodiment of the inventionis illustrated in FIGS. 9-12.

There is a definite relationship between the diameters d₁ and d₂ of thebearing section 20 of the fastener pin 10, the maximum expansiondiameter d₉ of the expansion section 86 and the diameter d₈ of the pilotsection 85 of the collet 11, the initial hole diameter D_(I) of theholes H, the recovered hole diameter D_(R) of the holes H after passageof the collet 11 therethrough, and the final interference average holediameter D_(f) when the fastener pin 10 is installed in the holes.Usually, the diameters d₁ and d₂ of the bearing section 20 of thefastener pin 10 are the controlling diameters since the average diameterd_(a) based on these diameters correspond to that of a standard sizefastener. Thus, if it is desirable to place the bearing section 20 ofthe fastener pin 10 into an average interference fit of a prescribedamount, such as 0.002 inch, then the recovered hole diameter D_(R) mustbe 0.002 inch less than the average diameter d_(a) of the bearingsection 20 of the fastener pin 10. When the material of the work piecesP is known, the recovered hole diameter D_(R) can be predicted and thusdetermine the maximum expansion diameter d₉ of the expansion section 86of the collet 11. The diameter d₉ can be calculated to be that amountlarger than the recovered hole diameter D_(R) to make the recovered holediameter D_(R) the desired amount smaller than the average diameterd_(a) of the bearing section 20 of the fastener pin 10 for theinterference fit. Once the diameter d₉ is determined, the initial holediameter D_(I) can be determined and is that amount less than themaximum expansion of the holes as determined by the diameter d₉ by whichit is desired to expand the holes. If it is desirable to coldwork theholes, the amount the holes H are to be expanded is set by the availablecoldworking data. Once the initial hole diameter D_(I) is determined,this determines the diameter d₈ on the pilot section 85 of the collet11. It is also to be understood that the difference between thediameters d₁ and d₂ is limited by the maximum amount of recovery of theholes H after passage of the collet 11 if an interference fit isdesired. For instance, if the average diameter d_(a) were 5/16 inch forthe fastener pin 10 to be installed and it is desirable that the bearingsection 20 is to be an average interference of 0.002 inch through7075-T6 aluminum, then the diameter d₉ should be 0.315 inch ifcoldworking is desired to produce un unrestrained recovered holediameter D_(R) of 0.308 inch where the initial hole diameter D_(I) is0.300 inch. Thus, the diameter d₈ of the pilot section 85 on collet 11should be just slightly less than the initial hole diameter D_(I) or0.299 inch. Since it is desirable to have the entire hole surface inbearing contact with the surface 22 on the bearing section 20 offastener pin 10, the diameter d₁ should be 0.311 inch and diameter d₂should be 0.309 inch to give an average interference of 0.002 inch. Therelationship between diameter d₁ and diameter d₂ will remain the sameregardless of the grip length of the fastener. For sake of illustration,the relative dimensions have been exaggerated in the drawings.

As seen in FIG. 9, the collet 11 has been placed around the supportsection 41 on the pintail portion 14 of fastener pin 10 with the drivingface 24 on the leading end of the bearing section 20 bearing against thetrailing face 92 on the trailing end of the collet 11. The leading endof the pintail portion 14 of the fastener pin 10 is inserted through theholes H in the work pieces P so that the leading end of the pintailportion 14 is projecting from the offset OS of the work pieces P and thepilot section 85 of the collet 11 is within the holes H adjacent thenear side NS of the work pieces P. When a countersunk head fastener pin10 is used, an appropriate countersink CS would be provided in the nearside of the work pieces P. It will be noted that the leading expansionsurface 89 is now bearing against the near end of the holes H.

As illustrated in FIG. 10, the nose assembly N of a conventionallockbolt installation gun is inserted over the projecting end of thepintail portion 14 whereby the internal jaws in the nose assembly N gripthe pintail portion 14, and when the gun is activated, the nose assemblyN pulls the collet 11 through the holes with the bearing section 20immediately following the collet 11 through the holes until the fastenerpin 10 is in the holes with the head 21 bearing against the work pieces.It will be noted that the trailing daimeter d₁₀ of the collet 11 isslightly larger than the leading diameter d₁ of the bearing section 20so that the leading end of the bearing section 20 can pass into theholes without damaging the hole surface. As the collet 11 moves throughthe holes H, the holes are expanded over the expansion surface 89 out tothe land surface 90 and then are allowed to recover along thecontraction surface 91 under the influence of the inward compressiveforces on the material immediately adjacent the holes after expansion,the compressive forces exerted thereon by the material of the workpieces farther away from the holes. This causes the holes to recovertoward the unrestrained recovered diameter D_(R) shown by dashed linesin FIG. 11. As the holes recover, they are prevented from fullyrecovering by the bearing section 20 immediately following the collet 11to form the interference fit. After the collet 11 has been movedcompletely through the holes H as seen in FIG. 11, it will be seen thatthe hole has a final diameter corresponding to the diameters d₁ and d₂of the bearing section 20 of fastener pin 10. Because the bearingsection 20 prevents the holes from fully recovering, it will be seenthat the bearing section 20 is in interference fit with the holes H. Ifthe nose assembly N is of the self-releasing type, the nose assembly canbe removed from the pintail portion 14 and then the collet 11 slidablyremoved therefrom as illustrated being done in FIG. 11. The pintailportion 14 is removed by exerting a lateral rather than axial forcethereon to fracture breakneck section 15 to prevent the loss of preloadon the final joint.

Experimental data has shown that the force required to move an expansiontype tapering surface through holes is inversely proportional to theslope. Because the average slope of the expansion surface 89 on thecollet 11 is much greater than the slope on the bearing section 20 ofthe fastener pin 10, it will be seen that the force required to removethe fastener pin 10 from the holes by movement toward the head issignificantly greater than the force required to force the fastener pin10 into the holes with the collet 11 immediately preceeding same as thefastener pin 10 moves toward the pintail portion 14. Thus, the forces ofthe work pieces P on the fastener pin 10 will always try to further seatthe fastener pin 10 in the holes. It will be further seen that if thetension load on the joint is low such as in a shear application, theneed for a locking device such as a nut or swagable collar iseliminated. As long as at least the major portion of the bearing surface22 on the bearing section 20 is in interference bearing contact with theholes H, the fastener will be retained in the holes. In some instancessuch as that shown in FIG. 13, it may be desirable to leave a slightclearance c about the bearing section 20 of the fastener where thecountersink CS forms a sharp edge on thin sheet material. This can beacommplished by adjusting diameter d₁ or the hole diameter D_(I). Still,however, a major portion of the bearing surface 22 is in bearing contactwith the holes H to retain the resulting fastener portion 12 inposition.

FIGS. 19 and 20 show the first and second modifications of the fastenerpin 10' and 10" installed. It is to be understood that thesemodifications would be installed in the same manner as the fastener pin10 using the collet 11 and the dimensional relationships for the reversetaper portion 22_(RT) of these modifications would remain similar tothose described.

FIG. 25 illustrates the third modified fastener pin 10_(I) beinginstalled. After pin 10_(I) is installed, the pintail portion 14_(I)with expansion member 11_(I) is removed from fastener portion 12 byfracturing the breakneck section 15_(I).

The installation of the second embodiment of the fastener pin 110 isillustrated in FIG. 14 with the dimensional relationship between thebearing section 120 and the collet 111 being the same as those describedfor pin 10 and collet 11. It will further be noted that the diameter d₁₁of the secondary grip adjustment surface 125 would be no greater thanthe maximum expansion diameter d₉ of the collet 111 so that the gripadjustment section 125 can pass into the holes H without galling. Also,the offside OS of the work pieces P will fall somewhere along the gripadjustment surface 125 and that this grip adjustment surface 125 servesto further increase the force required to remove the fastener portion 12of the fastener pin 10 from the holes H after installation. The modifiedfastener pin 110 of FIG. 5 would be installed similarly.

FIG. 15 illustrates the third embodiment of the fastener pin 210 beinginstalled with the collet 11 thereon. That step of installationillustrated in FIG. 15 would be performed the same as that described forthe fastener pin 10. After the fastener pin 210 has been seated, thenose assembly N and the collet 11 are removed and then the pintailportion 214 broken from the leading end of the engagement section 225 atthe breakneck section 215 with a lateral force. The nut 300 is thenscrewed down on the engagement section 225 so that the bearing face 306of the nut 300 bears against the offside OS of the work pieces P totorque the fastener portion 212 into position. It will be noted that thediameter d₄ of the engagement section 225 is considerably smaller thanthat normally associated with the particular size fastener correspondingto the bearing section 220. For instance, if the bearing section 220corresponds to a 5/16 inch fastener, then the diameter d₄ wouldcorrespond to that of the diameter of the engagement section of a 1/4inch fastener. It will also be noted that a standard nut could bescrewed onto the threads 226 if a washer is used to clear the leadingend of the bearing section 220.

The installation of the modification to the third embodiment of theinvention illustrated in FIG. 8 is best seen in FIG. 17 where a swagablecollar SC has been placed around the engagement section 225' preceededby a washer W to clear the leading end of the bearing section 220 asdescribed above. The swagable collar SC is illustrated as being swagedinto position in FIG. 17 as would normally complete the installationoperation. Finally, the pintail portion 214 would be broken at thebreakneck section 215 with a lateral force rather than an axial force toprevent loss of the preload on the resulting fastener joint.

FIG. 18 illustrates the fourth embodiment of the fastener pin 410 withits expansion collet 411. FIG. 18 shows the fastener pin 410 after ithas already been placed in the holes H and the collet 411 is beingremoved therefrom. It will be noted that, as the collet 411 preceeds thefastener portion 412 of the fastener pin through the holes, the holes Hrecover to the diameter D_(R) and is then re-expanded over the lead-insurface 426 to place the holes H into interference with the bearingsurface 422 on the bearing section 420 of the fastener pin 410. Thepintail portion 414 may be broken with a lateral force at this point inthe installation and then a conventional nut screwed on the engagementsection 425 or the pintail portion 414 may be left intact and used totension preload the joint independently of the nut and the nut usedsimply to lock in the prescribed preload in the resulting joint.

METHOD OF FABRICATION

FIGS. 21-23 illustrate a method of fabricating the fastener pins of theinvention. As seen in FIG. 21, the fastener pin FP is made using twocomponents, a fastener blank FB that will form the fastener portion ofthe finished fastener pin and a pintail blank PB that will form thepintail portion of the finished fastener pin. By using two componentblanks, the blanks may be made of dissimilar materials as will becomemore apparent so that the fastener blank FB may be made of a highstrength, relatively expensive material as required by the structuraldesign consideration of the finished joint and the pintail blank PBwhich is discarded after the installation is complete may be made out ofa relatively inexpensive material sufficiently strong to pull thefinished fastener pin into the holes in the work pieces.

The fabrication method utilizes the inertia welding principle employinga combination of relative rotation between the parts, axial force andinertia to join the blanks FB and PB to each other without the use offiller materials or exotic atmosphere. The frictional interface betweenthe blanks FB and PB generate the heat needed to weld the blankstogether.

The fastener blank FB has a rough sized bearing section BS and a roughsized head section HS that are slightly oversized to the finishedsections so that the finished sections can be formed therefrom. Theleading end of the fastener blank FB may have a circular projection CPon the face thereof which is coaxial about the central axis A_(p) of thefastener blank FB. The pintail blank PB has a rough sized pullingsection PS thereon from which the fulling section on the pintail will beformed and a rough sized support section SS thereon from which thesupport section on the pintail will be formed. It will thus be seen thatthe trailing end E_(p) of the pintail blank PB is oriented generallynormal to the central axis A_(p) of the pintail blank PB and the leadingend E_(f) of the projection CP on the fastener blank PB is also orientedgenerally normal to the central axis A_(p) of the fastener blank FB.With the fastener blank FB and the pintail blank PB oriented coaxiallyas seen in FIG. 21, relative rotation is generated between the blanks FBand PB with the trailing end E_(p) of the pintail blank PB facing theleading end E_(f) on the projection CP of the fastener blank FB. This isusually performed by holding one of the blanks FB or PB stationary whilethe other blank is rotated at a high rate of speed in a flywheel of aprescribed mass. The pin-tail blank PB is illustrated in FIG. 21 as thatblank being rotated, however, it is to be understood that the pintailblank PB may be held stationary while the fastener blank FB is rotatedor the blank FB and the blank PB may be counter-rotated. Usually, theblank being rotated is housed within a flywheel which has a certain massand after the blank such as the pintail blank PB is rotated up to aprescribed speed, the rotation driving force is removed and the blanksFP and PB are forced together so that the trailing end E_(p) of thepintail blank PB frictionally engages the leading end E_(f) of fastenerblank FB. As the kinetic energy of the flywheel carrying the pintailblank PB is absorbed at the frictional interface between the ends E_(p)and E_(f) and dissipated as heat at this interface, the heat generatedby the kinetic energy is sufficient to weld the ends E_(p) and E_(f)together by the time the kinetic energy of the spinning flywheel hasbeen absorbed at the interface. The blanks are illustrated in FIG. 22 ashaving been welded together using this technique. It will be noted, thatin the welding process, welding flash material WF is extruded out aroundthe welded joint. The fastener pin blank FP is now ready for subsequentfinishing operations with the pintail blank PB integral with the leadingend of the fastener blank FB through the welded joint J.

While different techniques may be used to finish the fastener pin blankFP, FIG. 23 shows the blank FP being partially finished by a grindingprocess. A grinding wheel GW which has an external configurationcomplimentary to the desired configuration of the support section of thepintail blank PB, the bearing section of the fastener blank FB and thehead of the fastener blank FB is used to grind away the flash materialWF, size the support section SS on the pintail blank PB to form thesupport surface 45, form the breakneck groove 55 at the juncture betweenthe pintail blank PB and fastener blank FB, usually centered on the weldjoint J between the two blanks, size the bearing section to form thebearing surface 22 on fastener blank FB and finish the head section toform the head 21. It is to be understood that while the blank for thefastener pin 10 is illustrated, this technique could likewise be usedfor the other fastener pins illustrated with the weld being made at thatposition on the blank at which the breakneck groove is to be located.After the grinding operation, the ridges and grooves may be rolled inthe pulling section PS of blank PB to finish the fastener pin.

While specific embodiments of the invention have been disclosed herein,it is to be understood that full use may be made of modifications,substitutions and equivalents without departing from the scope of theinvention.

I claim:
 1. A method of installing a fastener through work pieces toform a joint, the fastener having an enlarged head integral with thetrailing end of a bearing section with a bearing surface thereontapering from a bearing major prescribed diameter at the leading end ofthe bearing section to a bearing minor prescribed diameter trailing saidbearing major diameter where the bearing minor diameter is less than thebearing major diameter, comprising the steps of:(a) forming generallyaligned holes through the work pieces of a prescribed substantiallyconstant initial diameter smaller than the major diameter of the bearingsection such that the material of the work pieces will cause the holesto rebound to an unrestrained recovered diameter smaller than the majordiameter of the bearing section of the fastener after the holes havebeen expanded at least to the major diameter of the bearing section ofthe fastener; (b) locating a separate expansion member coaxially withthe fastener so that the trailing end of the expansion member abuts theleading end of the bearing section of the fastener where the expansionmember defines an expansion surface thereon concentric about the commonfastener and expansion central axis with the expansion surface having aleading minor diameter at least as small as the initial hole diameter, amajor expansion diameter trailing the leading minor expansion diameterat least as large as the bearing major diameter, and a diameter at thetrailing end of the expansion member abutting the leading end of thebearing section of the fastener equal to the diameter of the leading endof the fastener abutting the trailing end of the expansion member sothat the bearing section of the fastener and the trailing end of theexpansion member form a substantially continuous surface across theabutting ends; (c) while maintaining the fastener and expansion membercoaxially located, forcing the fastener into the holes with the fastenerforcing the expansion member through the holes immediately preceding theleading end of the bearing section of the fastener to keep the leadingend of the fastener in abuttment with the trailing end of the expansionmember so as to selectively expand the thusly formed holes to the majorexpansion diameter of the expansion surface such that the holes willcontract to an unrestrained recovered diameter smaller than the bearingmajor diameter of the bearing section of the fastener after expansionand insert the bearing section of the fastener through the holes whileexpanded until the head of the fastener bears against the work pieceswith the material of the work pieces about the holes moving smoothlyover the abutting ends of the bearing section of the fastener and theexpansion member without damaging the work pieces about the holes sothat the work pieces contract into bearing contact with at least themajor portion of the bearing surface on the bearing section of thefastener within the holes to grip the bearing section of the fastener,hold the fastener in place in the work pieces; and (d) after thefastener is in the holes with the bearing section being gripped by thework pieces, removing the expansion member from the leading end of thebearing section of the fastener.
 2. The method of claim 1 wherein thebearing minor diameter is selected so that it is larger than theunrestrained recovered diameter of the holes after expansion in orderfor the work pieces to contract into bearing contact with substantiallyall of the bearing surface of the bearing section of the fastener withinthe holes in step (c).
 3. The method of claim 1 wherein step (c) furtherincludes expanding the holes to a diameter sufficient to coldwork thematerial of the work pieces about the holes.